Low-profile dome-shaped multi-lens system

Abstract

A multi-lens system provides a plurality of sensitive areas of even size over a wide panoramic field of view and reduces an exposure height of the system above an installation plane, yet assuring successful motion detection. The system has a dome-shaped shell with a plurality of convex lenses for collecting infrared radiation from the panoramic field of view to an optical detector positioned in a focal region. The lenses are distributed over a wide solid angular range to give the discrete sensitive areas. The focal region is offset towards a vertex of the shell from a point where optical axes of the outermost lenses at a maximum solid angle about the center axis intersect with each other. Thus, the outer lens at a greater angular disposition has a greater distance to the detector so that it could define its own sensitive area closer in size to the adjacent sensitive area defined by the adjacent lens at a less angular disposition, enabling to equalizing the discrete sensitive areas. Further, the exposure height of the system i.e., a vertical distance between the vertex of the shell and the outermost lens is reduced to achieve a low-profile installation design. The lens at a greater angular disposition about the center axis is set to have a greater focal length so as to provide an effective image spot in the focal region for detection of infrared radiation through each lens by the detector, thereby assuring a consistent motion detection over a widely distributed sensitive areas.

Description

1. Field of the InventionThe present invention is directed to a low-profile dome-shaped multi-lens system, more particularly to such a system for collecting infrared radiation from a panoramic field of view to an optical detector for motion detection.2. Description of the Prior ArtU.S. Pat. No. 4,930,864 discloses a prior lens system covering a panoramic field of view for infrared motion detection within a wide detection range. The system comprises a semispherical shell provided with a plurality of convex lenses arranged to define a plurality of sensitive areas in the panoramic field of view for collecting infrared radiation from each sensitive area to an optical detector. Upon receiving infrared radiation from persons or objects passing through the sensitive areas, the optical detector provides a signal of fluctuating radiation level which is processed by an associated electronic circuitry for detecting a motion of the persons or objects. This lens system is designed to give an equ...

AI Technical Summary

Benefits of technology

The multi-lens system in accordance with the present invention comprises a dome-shaped shell formed with a plurality of convex lenses for collecting infrared radiation from a panoramic field of view to an optical detector positioned in a focal region. The dome-shaped shell has a vertex and a center axis extending through the vertex in a direction perpendicular to a tangent of the vertex. A plurality of the convex lenses each having an optical axis are distributed over a wide solid angular range about the center axis in order to provide a plurality of discrete sensitive areas within the panoramic field of view for surveillance by the detector. The focal region in which the detector is disposed is defined at a position offset towards the vertex from a point where the optical axes of the outermost lenses at a maximum solid angle about the center axis intersect with each other. With this result, the distance between the optical detector and the lenses is made longer for the outer lens disposed at a greater angle about the center axis. Thus, the outer lens positioned at a grater angle could define a corresponding discrete sensitive area of which size is closer to the adjacent sensitive area defined by the adjacent lens at a less angular disposition, in very contrast to the prior configuration in which all of the lenses are disposed at the same distance from the detector. Therefore, it is made possible to provide a plurality of discrete sensitive areas of even size over the panoramic field of view. In addition, provided that the same panoramic field of view is intended, the distance between the vertex of the shell and the outermost lens along the center axis can be made smaller than in the prior art configuration in which all the lenses are spaced from the detector at the same distance or radius, thereby contributing to reduce the exposure height of the shell when mounted on the ceiling or the like to give a low-profile structure to the lens system.

Notwithstanding the above low-profile structure, the convex lens at a greater angular disposition about the center axis is designed to have a greater focal length in order to provide a substantial image spot in the focal region for detection of the infrared radiation through each of the convex lens by the optical detector, thereby assuring a consistent motion detection over a widely distributed sensitive areas.

Each of the lenses defines a lead axis which passes through the principal point of each lens and through a common point in the focal region. The lead axis for each lens is inclined at an angle with respect to the center axis for the same lens within a common plane. Based upon the finding that the motion detection could be successfully made even with a small deviation between the lead axis and the optical axis, the lens system can be designed without imposing a strict control of aligning the optical axis with the lead angle for each lens, thereby being given sufficient design flexibility for simple lens configuration with attendant ease of fabrication.

In a preferred embodiment, the dome-shaped shell is formed on its inner surface with a plurality of convex faces each forming each one of the convex lenses with a corresponding portion of an outer surface of the shell. The lenses are arranged in a closely adjacent relation with each other in such a manner that the convex face of the lens merges into the convex faces of the adjacent lenses. Whereby, no substantial dead-area is formed between the adjacent lenses to eliminate otherwise developed optical loss and therefore enhance collectivity of radiation from within the panoramic field of view.

Problems solved by technology

The difference becomes more critical as the sensitive areas are distributed over a wider angular range, which makes it difficult to determine a precise motion detection at the peripheral sensitive areas as is possible for the center sensitive areas.

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